Molding compound



Patented Apr. 14, 1942 Frank J. Grotenand James B.

Lower, Stamford,

Conn., assignors to American Cyanamid Company, New York, Y., acorporation of Maine No Drawing. Application August 1, 1940,

Serial No. 349,300 12 Claims. 280-45) This invention-relates to animprovement iu.

' the new class of resinous molding compounds 'described'inourc'opending application Serial No.

256,772, filed February 16, 1939, now .Patent No. 2,229,291, datedJanuary 21, 1941. The invention includes the improved molding resinsthem selves, their methods of preparation, and the molded productsobtained therefrom.

In theabove identified application we have described a class of moldingcompounds prepared from a new type of synthetic resin which 'isanaldehyde condensation product of the material obtained upon heatingdicyandiamide with a phenol until substantial quantities of'. ammoniaare given off and most of the dicyandiamide is converted into .cycliccompounds. The molded products described in that applicaheat andpressure, without the addition of any objects having an even bettersurface appearance than those obtainable by using an acid catalyst, asdescribed in our prior application. Moreover,

othercatalyst or curing agent whatsoever, into the moldability of ournew resins extends over tion :are prepared by .mixing these heat-treateddicyandiamide-phenol resins with small quantities of an acidic curingagent, together with lubricants and fillers, and molding the resulting"compound under heat and pressure for suitable periods of time.

a much wider range than is possessed by our earlier compounds, whichmeans that eithera rapid cure or a slower cure with better flowproperties in the mold can be obtained at will. Since the moldingcompound contains no curing material other than the alk ali its ageingproperties are excellent and it can be stored for many months withoutimpairing its molding properties.

We have found that the principles of .our invention are equallyapplicable to the preparation of thermosetting resins from any of thegrades of phenol describ in our earlier application identified above.In'o'ther words, we have found that heat treated mixtures of'dicyandiamide with synthetic phenol, 395 phenol, 82% phenol,

- and lower grades of phenols containing cresols,

Ourpresent invention relates more particu-.

' larly to an improvement in the steps of condensing the heat-treateddicyandiamide-phenol mixture with formaldehyde or other'aldehyde and thesubsequent preparation of molding compounds. In our prior application.we pointed out that the formaldehyde should preferably be ad- H. of9.1-9.5 'before condensing it iusted to a with the eat-treateddicyandiamide-phenol mixture, in order to avoidgelation of the resin,but we stated that during the aldehyde condensation reaction a drop inthe pH' to 7.2-7.6 would benoted.

Further investigations .have shown that this drop in pH during theformaldehyde condensation was due to the fact that we employed sodiumhydroxide ,for neutralizing the formaldehyde.

or no bufiering action-and also causes the.de-

.This material, like other free alkalies, has little composition offormaldehyde to formic acid' and methanol, which isthe well-knownCannizzaro reaction. The formic acid produced by this reaction causedthe-rapid drop in pH that was noted during the formaldehydecondensation.

By replacing the sodium hydroxide with other alkalies having abuifering-action we have suc- I ceeded in maintaining the pH at aconstant value between about 9.1 and 9.5 throughout the formaldehydecondensatiomand we have obtained a new type of' resin having entirelydifferent and r unexpected properties. This resin can be mixed withfillers and lubricants and molded under xylenols and the like, can becondensed with formaldehyde,'acetaldehyde, benzaldehyde, fur-.

fural and .other reactive aldehydesat a pH of about 9.1 to 9.5 to formresins, all of which are capable of beingcuredat ordina'ry moldingtemperatures of ISO-175 F. or higher without the addition of catalystsor curing agents. The following is .a description of the phenols whichwe have used in preparing our new resins:

(1') Synthetic phenol. This is the C. Pimaterial and consists ofpractically 100% CsHsQH.

(2) 395 phenol. This is the highest grade of coal 'tar phenolobtainable. It contains .between 99 and 99.5% CsHsOH.

(3) 82% phenol. This material consists of 82% CsHsOH, 8-14% meta andpara-cresols and 4-10% o-cresol.

(4) Barrett No. 8 Cresol." A representative sample of-this materialcontains 0.25% o-cresol, 2.25% phenol, 73.5% of a mixture containing 60%meta and 40% para-cresol, 10.5% of a fractionconsisting of 20% meta. andpara-cresols,

60% 1.2.4 xylenol and 20% 1.3.5 xylenol and known as the :r1, fraction,and 13.5% of a fraction boiling between 204 C, and 210 .0.

Half of this fraction is meta and para-cresols and the other halfisthe\:c-1- fraction having the composition indicated above.

(5) fBarrett Cresylic Acid (212 C.) A top-- resentative sample of thismaterial contains 10.8% phenol, 1.2% o-cresol, 20% meta anclpara-cresols, 20%"a:-1-" fraction, 20% 1.2.4

in a jacketed kettle provided with an agitator and dicyandiamide isadded. The charge is heated with stirring to the reflux temperature ofthe phenol, which is about 181-212 C. and

maintained at these temperatures with agitation for about 2.5-5.5 hours.During this timeammonia is given off and is allowed to escape. The timeof heating can be shortened to 1.5 hours if an acid condensing agentsuch as anhydrous zinc chloride is added in amounts of 0.5% of theweight of the dicyandiamide, as described in the copending applicationof J. T. Thurston et al, Serial No. 301,766, filed October 28, 1939.

The time of heating influences the properties.

of the finished product. -We have found that upon continued heating asmuch as 0.2 mole of ammonia can be driven off for each mole ofdicyandiamide charged, but in most cases a shorter heating period andcorrespondingly reduced ammonia evolution is recommended. Ordinarily thebest results are obtained when from 0.13 to 0.18 mole of ammonia permole of dicyandiamide are liberated, but we have obtained resins of goodproperties with much shorter heating periods and i with the evolution ofas little as 0.07-0.10 mole of ammonia per mole of dicyandiamide. It issometimes desirable to carry out the refluxing in an atmosphere of aninert gas such as nitrogen or carbon dioxide in order to exclude oxygen.I

The amounts of dicyandiamide to be heated with the phenol may varybetween rather wide limits, depending on the characteristics desired inthe finished product. Ordinarily equimolecular ratios of phenoland-dicyandiamide are used, but where better heat resistance is desiredit may be advisable to employ 2 or 3 moles of dicyandiamide for eachmole of phenol.

After cooling the heattreated material tobelow 100 C. the product iscondensed with formal- Q dehyde, acetaldehyde, benzaldehyde or othersuitable aldehyde. The amount of aldehyde may vary from 2.7 to 5 molesfor each mole of the phenol-dicyandiamidei mixture. As has been stated,thi ldehyde should first be mixed with 'sufilcient a ounts of an alkalihaving bufiering' propertiesto raise the pH to about 9.1-9.5 andpreferably to about 9.3. Sodium and potassium carbonate are the bestcompounds that we have found for this purpose, but sodium silicate,sodium borate, and trisodium phosphate or their potassium equivalentsmay also be used. These or similar compounds may be added to thealdehyde as the dry solid or in solutions, using amounts sufli'cient toraise the pH to the desired figure. The condensation of the aldehydecontaining these butters with the heat-treated material is then carriedout by heating the charge to refluxing temperatures which are about96-98 C., and refluxing for about hour or longer, depending on thepurpose for which the resin is to be used. It will be noted that this isa much shorter time than is recommended for molding compounds whencaustic soda is used as the alkali.

After refluxing the charge for the desired period of time it isdehydrated. This step is preferably carried out by applying a vacuum tothe kettle such that most of the water can be removed at 72-76 C. Nearthe end point of the dehydration the temperature will riseto about95-110 C., depending on the type of resin and 5 time of reflux, and thecharge is poured at this temperature after the last of the water hasbeen evolved. It. cools to a hard,.brittle mass which will be clear ifnitrogen was used as the inert gas in the kettle but slightly cloudy ifcarbon dioxide was used.

To prepare the molding compound, the resin is preferably finely ground(150-300 mesh). It is then thoroughly blended with a lubricant such as amixture of calcium and zinc stearates, zinc l5 oleate or the like. Afiller such as wood flour. alpha-pulp, asbestos, diatomaceous earth,mica or similar material and a suitable amount of other at 135 C., for1.5 minutes when using awood flour filler and 1 to 3 minutes withalphapulp -filler and the resulting sheets are then ground to a particlesize suitable for molding which may be done with or without apreliminary pelleting.

An alternative process which may be employed -'in the preparation ofimpregnated sheets or in preparing molding compounds is to omit thevacuum dehydration leaving the resin in syrup form. This syrup may besoaked into absorbent paper sheets which are then dried and pressed outin a flat mold to make a laminated board.

Similarly, the resin syrup may b'epoured directly onto a blended mixtureof the filler, lubricant and dye in a Banbury mixer at temperatures oi"60-90". C. and mixed until the filler is thoroughly coated. The mass maythen be dried-with or without vacuum under controlled conditions untilsubstantially all the water is'removed after which it may be ground ifdesired.

The invention will be illustrated in greater de tail by the followingspecific examples. It should be understood, however, that these examplesare given primarily for purposes of illustration, and, that theinvention in its broader aspects is not limited thereto.

Example 1 Equimolecular quantities of dicyandiamide and 39.5,phenol are'heated and refluxed at atmospheric pressure for 4 hours. Shortly afterthe. heating is begun an evolution of ammonia is noted and the refluxingis continued until about i 0.10 to 0.18'mole, and preferably about 0.15mole,

' of ammonia have been givenofi for each mole of dicyandiamide charged.The mixture 'is then cooled to below 100? C.

1.85 lbs. of anhydrous sodium carbonate were added to 119.2 lbs. of 37aqueous formaldehyde solution, which was then mixed with lbs.

of the cooled reaction mixture described above.

The formaldehyde condensation was then carried out by refluxing themixture at 96-98 C. for

the pH of the mixture was 9.3, and the same value was also found whenthe condensation was com-- pleted. The condensation product was thendehydratedby heating under. a 21 inch' vacuum and the resin was cooledand ground to -300 mesh.

.A molding compound was prepared by. intimately mixing 400 parts of theground resin, 216 parts of alpha pulp and 3 parts of calcium stearate orother suitable lubricant. The mixture 0 about 30 minutes. At thebeginning of the reflux color.

was blended thoroughly and then compounded onsteam-heated diflerentialrolls at 100 and 135 C. for 0.75 to 2.5 minutes, depending on the flowdesired. After grinding to suitable particle size,

portions of the batch were molded into tumblers, using a steam-heatedpress at 150-160 C. The

, pieces were found -to have a light cream color, ex-

150 cc. of water for 30 minutes to. extract any free phenol that mightbe present. The water was then drained ofl.,-cooled to room temperature,and bromine water was added drop by drop to a cc. sample until it wassaturated as indicated by a yellow color. No precipitate was formed,indicating a complete absence of free phenol in the molded resin as thistest is very sensitive.

Example 2 23.6 parts by weight of dicyandiamide and 26.4 parts of 82%phenol arev heated and refluxed at atmospheric pressure with continuousagitation for 4 hours. Shortly after the heating is begun an evolutionof ammonia is noted, and

the refluxing is continued until about 0.15 mole of ammonia have been ofdicyandiamide charged. The mixture isthen cooled to below 100 C. I

60.8 parts of 37.5% formaldehyde solution given off for each mole areneutralized by the addition of sodium carbonate to a pH of 9.1. added tothe cooled reaction mixture and the formaldehyde condensationis carriedout with refluxing at 96--98 C. for about hour. The condensation productis dehydrated by heating under a 21 inch vacuum until all the water isremoved and the resin, upon cooling, is hard and brittle. The resin isthen cooled to room temperatures and ground to 150-300 mesh.

A molding compound is prepared by intimately mixing 400 parts of theresin, 400 parts of wood flour and 4' parts of calcium stearate withsuitable amount of dyestufl to give the required The mixture is blendedthoroughly and then compounded on steam-heated differential rolls at100-110 C. for 0.75 to 2.5 minutes, depending on the flow desired. Thematerial may then be ground leted if desired.

. Example 3 or other filler together with a lubricant. The resultingmolding compound is well suited for a largevariety of purposes, since itcan be molded to pieces which are fairly light in color 'and possessgood dielectric strength, excellent arc resistance and retain theirdimensions under the most extreme conditions of humidity.

Example 4 27, parts of Barrett Cresylic Acid (212 0.) and 18.5 parts ofdicyandiamide are heat-treated to suitable particle size and pel-- Thissolution is then .flour, or suitable amounts of diatomaceous earth.

as in Example 1 until about 0.13 mole of am- 1 monia areevolved for eachmole oi dicyandialdehyde the material obtained 3 amide. The product iscondensed with" 46 parts of 37.5%iormaldehyde solution neutralized withborax to a pH of 9.4 after which the resulting.

resin is dehydrated under a vacuum, cooled and ground to -300'mesh orfiner.

400 parts of the ground resinare mixedwith-an equal weight of wood flouror suitable amounts of other fillers such as mica, diatomaceous earth,cotton flock, etc., together with a lubricant such as calcium stearate.The resulting powder-can be cured in 1 minute under ordinary moldingconditions and is therefore a good general purpose molding compound forproducing any. type of molded article in which the lightest color is notrequired. It is particularly valuable for its good electrical propertiesand moisture resistance.

This is a continuation-in-part of our copending application, Serial No.256,772. filed February 16, 1939. now Patent No.,2,229,291, datedJanuary- 21, 1941. o

We claimz l. A method of preparing a thermos'ettingresin capable ofbeing cured without further addition of catalyst which comprisescondensing with an aldehyde the material obtained upon heatingdicyandiamide and a phenol until from.0.07 to 0.18 mole of ammonia permole of dicyandiamide are evolved while'maintaining the and 9.5throughout the aldehyde condensation.

2. A method of preparing a thermosetting resin capable of being curedwithout further addition of catalyst which comprises condensing with anupon heating dicyandiamide and a phenolic mixture containing an alkylphenol untilfrom .07 to 0.18 mole of ammonia per mole of dicyandiamideare evolved while maintaining the pH at a relatively constant valuebetween about 9.1 and 9.5 throughout the aldehyde condensation.

3. A method oi preparing a thermosetting resin capable of being curedwithout further ad dition of-catalyst which comprises condensi'ngr I,

with Ian aldehyde the material obtained upon heating dicyandiamide and acresol until from .07 to 0.18 mole of ammonia per mole of dicyandiamideare evolved while maintaining the pI-li at a relatively constant valuebetween about 91.1 and 9.5 throughout the aldehyde condensat on.

4. A method of preparing a thermosetting resin capable of being curedwithout further addition oi catalyst which comprises condensing with analdehyde the material obtained upon heating dicyandiamide and 82% phenoluntil from 0.13 to 0.18 mole of ammonia per mole of' dicyandiamide areevolved while maintainingthe pH at a, relatively constant value betweenabout 9.1 and 9.5 throughout-the aldehyde condensation.

5. A synthetic resin of the thermosetting type capable of beingcured'without further addition of catalyst. said resin being thecondensation product. of an aldehyde with the material obpH at arelatively constant value between about 9.1

from .07 to 0.18 mole oi ammonia per mole of dicyandiamide are evolvedwhile maintaining the pH at a relatively constant value between about9.1 and .95 throughout the aldehyde condensation.

'7. A Synthetic resin of the thermosetting type capable of being curedwithout further addition of catalyst, said resin being the condensationproduct of an aldehyde with the material obtained upon heating a mixtureof dicyandiamide and a cresol until from .07 to 0.18 mole of am- 'moniapermole of dicyandiamide are evolved while maintaining the pH at arelatively constant value-between about 9.1 and 9.5 throughout thealdehyde condensation.

8. A synthetic resin of thethermosetting type capable of being curedwithout further addition of catalyst, said resin being the condensationproduct of an aldehyde with the material obtained upon heating a mixtureof dicyandiamide and 82% phenol until from .07 to 0.18 mole of ammoniaper mole of dicyandiamide are evolved while maintaining the pH at arelatively constant value between about 9.1 and 9.5 throughout thealdehyde condensation.

'9. A molding composition comprising a filler and a synthetic resin ofthe thermosetting type capable of being cured without further additionof catalyst, said resin being the condensation product of an aldehydewith the material obtained upon heating a mixture of dicyandiamide and aphenol until from .07 to 0.18 mole of ammonia per mole of dicyandiamideare evolved while maintaining the pH at a relatively constant valuebetween about 9.1 and 9.5 throughout the aldehyde condensation.

10. A molding composition comprising a filler and a synthetic resin ofthe thermosetting type capable of being cured without further additionof catalyst, said resin being the condensation product of an aldehydewith the material obtained upon heating a mixture of dicyandiamide and aphenolic mixture containing an alkyl phenol until from .07 to 0.18 moleof ammonia per mole of dicyandiamide are evolved while maintaining thepH at a relatively constant value between about 9.1 and 9.5 throughoutthe aldehyde condensation.

11. A molding composition comprising a filler and a synthetic resin ofthe thermosetting type capable of being cured without further additionof catalyst, said resin being the condensation product ofan aldehydewith the material obtained upon heating a mixture of dicyandiamide and acresol until from .07 to 0.18 mole of ammonia per mole of dicyandiamideare evolved while maintaining the pH at a relatively constant valuebetween about 9.1 and 9.5 throughout the aldehyde condensation.

12. A molding composition comprising a filler and a synthetic resin ofthe thermosetting type capable of being cured without further additionof catalyst, said resin being the condensation product of an aldehydewith the material obtained upon heating a mixture of dicyandiamide and82% phenol until from .07 to 0.18 mole of ammonia per mole ofdicyandiamide are evolved while maintaining the pH at a. relativelyconstant value between about 9.1 and 9.5 throughout the aldehydecondensation.

FRANK J. GROTEN. JAMES H. LOWER.

